1. Field of the Invention
The present invention relates generally to automatic breast pumps. More specifically, the invention relates to apparatus and related methods for extracting milk from a human breast using adjustable controls that simulate the action of a nursing infant.
2. Description of Related Art
Most prior art breast pumps designed for extracting milk are concerned only with controlling the rate at which a negative pressure is applied to the breast and, in some cases, the amount of negative or vacuum pressure. An example of an electric breast pump which does more than this is illustrated in the U.S. Pat. No. 6,383,163 granted May 7, 2002 to two of the three named joint inventors of the present invention. The disclosure of U.S. Pat. No. 6,383,163 is expressly incorporated herein by reference.
Although the prior art breast pumps and, specifically, the prior art breast pump described and claimed in U.S. Pat. No. 6,383,163 are effective, they also have a number of shortcomings. For example, most prior art breast pumps only allow a mother to express her milk by applying a uniform vacuum pressure (or vacuum pressure profile) to the face of the breast. This simple approach does not effectively simulate the natural suckling of a nursing infant. Without effective simulation, the pump does not extract the milk as efficiently as possible. As a result, a longer pumping period is required, which increases the physical demands on the mother. These demands may discourage working mothers, or mothers still recovering from childbirth, from thoroughly completing the expression. Incomplete or improper expression of the milk may lead to engorgement of the breasts, mastitis, or infection.
In a natural suckling cycle, refractory time of the breast plays an important role in optimizing the efficiency of milk extraction. The refractory time is that part of the nursing cycle that begins after milk has been drawn from ducts within the breast, and ends when the depleted portions of the milk ducts refill. One invention that accounts for this refractory time is disclosed in U.S. patent application Ser. No. 10/644,199, assigned to the assignee of the present invention. The '199 application discloses a breast pump that draws a vacuum in periodic pulses at a frequency that may be adjusted by the mother to track her physiological refractory time.
Nursing an infant, however, is a biological process that is not so easily modeled with mathematical precision. Many conditions can change during expression of the milk. Perhaps the most obvious example is the onset of the let-down, or milk-ejection reflex. Research has shown that prior to let-down, an infant will suck at an elevated rate in the range of 72 to 120 sucks per minute. After let-down, when a satisfactory flow of milk is obtained, the infant relaxes the rate down to around 60 sucks per minute. The vacuum drawn by a suckling infant may vary between 18 mmHg and 200 mmHg. Prior to let-down, an infant typically applies a greater suction force than after let-down. In addition, as the store of milk in the alveoli diminishes, the infant may apply a higher suction force to sustain the flow.
The optimal refractory times, vacuum pressures, and vacuum pressure profiles will vary among different mothers. What is needed, then, is a breast pump that can be easily customized to optimize the efficiency of expression over a wide range of conditions.